Vortices in spatially inhomogeneous superfluids

Daniel E. Sheehy, Leo Radzihovsky
2004 Physical Review A. Atomic, Molecular, and Optical Physics  
We study vortices in a radially inhomogeneous superfluid, as realized by a trapped degenerate Bose gas in a uniaxially symmetric potential. We show that, in contrast to a homogeneous superfluid, an off-axis vortex corresponds to an anisotropic superflow whose profile strongly depends on the distance to the trap axis. One consequence of this superflow anisotropy is vortex precession about the trap axis in the absence of an imposed rotation. In the complementary regime of a finite prescribed
more » ... ion, we compute the minimum-energy vortex density, showing that in the rapid-rotation limit it is extremely uniform, despite a strongly inhomogeneous (nearly) Thomas-Fermi condensate density ρ_s(r). The weak radially-dependent contribution (∝∇^2ρ_s(r)) to the vortex distribution, that vanishes with the number of vortices N_v as 1/N_v, arises from the interplay between vortex quantum discretness (namely their inability to faithfully support the imposed rigid-body rotation) and the inhomogeneous superfluid density. This leads to an enhancement of the vortex density at the center of a typical concave trap, a prediction that is in quantitative agreement with recent experiments (cond-mat/0405240). One striking consequence of the inhomogeneous vortex distribution is an azimuthally-directed, radially-shearing superflow.
doi:10.1103/physreva.70.063620 fatcat:nwkdlvvqwzgbnnkt5zvgitno74